1. Field of the Invention
The present invention relates generally to a shielding system for a printed circuit board, and in particular, to a shielding system having an integral shielding enclosure with a fixed cover that may be permanently removed, and a replacement cover for attaching thereto.
2. Description of the Related Art
As is well known in the prior art, selected electric or electronic parts on a printed circuit board radiate electromagnetic waves which thereby cause noise or unwanted signals to appear in adjacent components on the printed circuit board or electric or electronic parts and devices existing in the vicinity of the printed circuit board. Accordingly, it is highly desirable to provide shielding for electronic components of printed circuit boards such as those found in radio transmitters, radio receivers, computers and other electronic devices that use circuitry that emits or is susceptible to electromagnetic radiation. It is known that these components can be shielded to reduce undesirable electromagnetic interference and/or susceptibility effects with the use of a conductive shield that reflects or dissipates the electromagnetic charges and fields. Such shielding may be grounded to allow the offending electrical charges and fields to be dissipated without disrupting the operation of the electronic components enclosed within the shield.
A variety of devices have been utilized for shielding electronic components, but these prior art devices have not been entirely satisfactory since they do not allow for easy access to the underlying electronic component after the installation of the shield.
For example, a conventional metal shield cover, or can, is mounted to a printed circuit board by using fasteners appropriate for the purpose. Thereafter, the metal shield is soldered or welded to selected grounding strips on the printed circuit board at selected locations of its side walls. Using solder or welding to mechanically hold and electrically connect the metal shield to the printed circuit board permanently affixes the metal shield over the selected electronic component(s).
After assembling the completed printed circuit board, including the required metal shields, the printed circuit board will generally be subjected to a "burn-in" stage during which it is subjected to elevated temperature tests. If one of the electronic components should fail during the burn-in, however, that component must be replaced. Thus, it becomes necessary to desolder or unweld the metal shield from the printed circuit board in order to obtain access to the failed component and replace the same. This is very difficult to successfully accomplish and, more than likely, the entire printed circuit board will be destroyed.
In order to overcome this problem, shielding devices, such as that disclosed in U.S. Pat. No. 4,754,101 of the present assignee, the entire contents of which are hereby incorporated by reference, have included a separate wall enclosure and a removable cover. The cover is resiliently held in place by deflectable engagement prongs extending from an upper edge of the wall enclosure. The presence of the resiliently held cover allows access to the underlying electronic component, should the same be required, however, the manufacturing costs associated with the formation of the engagement prongs are also increased.
Accordingly, there exists a need for a shielding cover which can be soldered to the printer circuit board, but which still allows access to the underlying electronic component should it be necessary to replace, repair or otherwise adjust the same, and which can be inexpensively manufactured.